This is the o-ring (sealing ring) for the UMS 9-99cc engine, the nine-cylinder 99cc four-stroke radial from UMS.
The part itself is a general-purpose sealing ring used at several joints on the engine.
Why it is replaced: O-rings are consumables and harden with heat, so they are renewed rather than reused. Supplied as a pack of 10, which is how these small parts are normally bought — you rarely need just one.
Fitting note: Match material and size to the application — not all O-rings are fuel or oil resistant.




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